Aqueous polyurethane dispersions

Claim 1

A composition obtained by mixing an isocyanate-terminated, carboxyl group-containing prepolymer made by reaction of (A) 1 equivalent of an aliphatic diisocyanate with (B) total 0.6-0.8 equivalent of the following active hydrogen compounds: (a) α,α-dimethylolacetic acid or a homologue thereof, (b) a polymeric glycol selected from poly(alkyleneoxy) glycols and polyester glycols having a weight average molecular weight of about 400-3000, and (c) N,N'-dicyanoethylpoly(propyleneoxy)diamine having a number average molecular weight of about 200-2000; the amount of component (a) being about 0.08-0.25 hydroxyl equivalent per 100 g of total weight of all the reactants A and B, and the relative mole proportions of compounds (b) and (c) being about 30:70 to 70:30, with an aqueous solution of a sufficient amount of a tertiary amine free of substituents reactive with isocyanate groups to convert substantially all the carboxyl groups of the prepolymer to carboxylate ions, then chain-extending the prepolymer with about stoichiometric amount, based on free isocyanate groups, of a diamine having at least one hydrogen attached to each nitrogen atom.